U.S. patent application number 13/098730 was filed with the patent office on 2011-11-10 for image forming apparatus capable of detecting contact fusion, and relay control apparatus.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Eijiro ATARASHI.
Application Number | 20110274450 13/098730 |
Document ID | / |
Family ID | 44902008 |
Filed Date | 2011-11-10 |
United States Patent
Application |
20110274450 |
Kind Code |
A1 |
ATARASHI; Eijiro |
November 10, 2011 |
IMAGE FORMING APPARATUS CAPABLE OF DETECTING CONTACT FUSION, AND
RELAY CONTROL APPARATUS
Abstract
An image forming apparatus which can individually detect contact
fusion of relays in a circuit configuration in which the relays are
connected to respective both ends of a fixing heater. A first relay
and a second relay are each connected between a power source and
the fixing heater. The presence or absence of an input voltage to
the fixing heater is detected on paths from the first relay to the
fixing heater and from the second relay to the fixing heater. When
the input voltage is detected in a state in which the first relay
is on and the second relay is off, it is determined that the second
relay has failed. When the input voltage is detected in a state in
which the first relay is off and the second relay is on, it is
determined that the first relay has failed.
Inventors: |
ATARASHI; Eijiro;
(Toride-shi, JP) |
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
44902008 |
Appl. No.: |
13/098730 |
Filed: |
May 2, 2011 |
Current U.S.
Class: |
399/37 |
Current CPC
Class: |
G03G 15/80 20130101;
G03G 15/55 20130101; G03G 15/2039 20130101; G03G 15/205 20130101;
G03G 2215/2032 20130101; G03G 2221/1639 20130101; G03G 21/1685
20130101 |
Class at
Publication: |
399/37 |
International
Class: |
G03G 15/00 20060101
G03G015/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2010 |
JP |
2010-106404 |
Claims
1. An image forming apparatus comprising: a heater configured to be
supplied with electrical power from a power source; a first relay
and a second relay each configured to be connected between the
power source and said heater; a voltage detection unit configured
to detect presence or absence of an input voltage to said heater on
paths from said first relay to said heater and from said second
relay to said heater; and a relay control unit configured to output
control signals for turning on and off respective ones of said
first relay and said second relay, wherein said relay control unit
determines that said second relay has failed when the input voltage
is detected by said voltage detection unit in a state in which said
first relay is on and said second relay is off, and said relay
control unit determines that said first relay has failed when the
input voltage is detected by said voltage detection unit in a state
in which said first relay is off and said second relay is on.
2. A relay control apparatus included in an image forming apparatus
comprising a heater configured to be supplied with electrical power
from a power source, a first relay and a second relay configured to
be each connected between the power source and the heater, and a
voltage detection unit configured to detect presence or absence of
an input voltage to the heater on paths from the first relay to the
heater and from the second relay to the heater, comprising: a first
control unit configured to, before starting passage of electric
current through the heater, output a control signal to turn on the
first relay, and when the input voltage is not detected by the
voltage detection unit, output a control signal to turn on the
second relay; a first determination unit configured to determine
that the second relay has failed in a case where the input voltage
is detected by the voltage detection unit when the first relay is
turned on by said first control unit; a second control unit
configured to, before ending passage of electric current through
the heater, output a control signal to turn off the first relay,
and when the input voltage is not detected by the voltage detection
unit, output a control signal to turn off the second relay; and a
second determination unit configured to determine that the first
relay has failed in a case where the input voltage is detected by
the voltage detection unit when the first relay is turned off by
said second control unit.
3. A relay control apparatus according to claim 2, further
comprising a third determination unit configured to determine that
both the first relay and the second relay have failed when the
input voltage is not detected by the voltage detection unit after
the control signal is output by said first control unit so as to
turn on the second relay.
4. An image forming apparatus according to claim 1, wherein said
voltage detection unit comprises a zero cross detection
circuit.
5. An image forming apparatus according to claim 1, further
comprising: a switch unit configured to be disposed on a path for
supplying electrical power to said heater, and turn on and off said
first relay and said second relay according to the control signals
from said relay control unit; and a temperature detection unit
configured to detect a temperature of said heater and output a
temperature detection signal to said relay control unit, wherein
said relay control unit controls the temperature of said heater by
controlling said switch unit based on the temperature detection
signal.
6. An image forming apparatus according to claim 5, further
comprising a heater temperature abnormality detection unit
configured to determine whether the temperature of said heater is
higher than a predetermined temperature based on the temperature
detection signal output from said temperature detection unit,
wherein said heater temperature abnormality detection unit outputs
a control signal to turn off said first relay and said second relay
when determining that the temperature of said heater is higher than
the predetermined temperature.
7. An image forming apparatus according to claim 6, further
comprising an computation unit configured to perform logical
conjunction of the control signal from said heater temperature
abnormality detection unit and the control signal from said relay
control unit, wherein said computation unit outputs a signal to
turn off said first relay and said second relay based on the
control signal for turning off said first relay and said second
relay, which is input from one of said heater temperature
abnormality detection unit and said relay control unit.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an image forming apparatus
such as a copier or a printer, which forms images on recording
materials using an electrophotographic process, and a relay control
apparatus, and in particular to a power-feed path of a fixing
apparatus that thermally fixes unfixed toner formed and carried on
recoding materials.
[0003] 2. Description of the Related Art
[0004] Conventionally, for electrophotographic image forming
apparatuses, methods that heat and fix a toner image formed on a
recording sheet (heat fixing methods) have been commonly adopted,
and in particular, a method that brings a toner image into direct
contact with a rotary member having a heat source therein and fixes
the toner image has been in widespread use. As the heat source, a
halogen heater, a ceramic heater, an IH heating, and so on are
known, but all of them require so large amount of power as hundreds
of watts.
[0005] Moreover, with an increase in demand for power saving,
reducing standby electricity of image forming apparatuses has
become an important issue. Thus, there has been proposed an image
forming apparatus that raises fixing temperature at high speed by
an on-demand fixing technique using a ceramic heater, and thus
hardly requires standby electricity.
[0006] On the other hand, in such a fixing apparatus that raises
fixing temperature at high speed, the temperature of a fixing
heater abruptly rises, and it is thus important to quickly
interrupt electric current to the fixing heater when an abnormal
condition occurs. Moreover, to reliably interrupt electric current
to the fixing heater, it is necessary to stop supplying electrical
power to both ends of the fixing heater.
[0007] To stop the supply of electrical power to the fixing heater,
a mechanical relay is commonly used. The relay uses a contact, and
hence if the relay is repeatedly turned on and off, the contact may
be welded due to age deterioration. If the contact of the relay is
welded, electric current is passed through the fixing heater even
when the relay is turned off, and thus power feeding to the fixing
hearer does not stop, which may result in abnormal heating. To cope
with this, there has been proposed a method that a zero cross
detection circuit for detecting the presence or absence of input
voltage is provided in a stage subsequent to the relay, and when a
zero cross signal is output despite the mechanical relay being
instructed to turn off, it is determined that contact fusion of the
relay occurs (for example, see Japanese Laid-Open Patent
Publication (Kokai) No. 2002-296955).
[0008] The above described method makes it possible to detect
contact fusion of the relay by disposing the zero cross circuit in
the stage subsequent to the relay.
[0009] However, when relays are disposed at respective both ends of
the fixing heater, the zero cross circuit can detect contact fusion
only when contacts of both relays are welded, and the zero cross
circuit cannot detect contact fusion occurring in either one of the
relays. For this reason, the above described method is insufficient
in terms of safety.
SUMMARY OF THE INVENTION
[0010] The present invention provides an image forming apparatus
that is capable of, in a circuit configuration in which relays are
connected to respective both ends of a fixing heater, individually
detecting contact fusion occurring in the respective relays, and a
relay control apparatus.
[0011] Accordingly, a first aspect of the present invention
provides an image forming apparatus comprising a heater configured
to be supplied with electrical power from a power source, a first
relay and a second relay each configured to be connected between
the power source and the heater, a voltage detection unit
configured to detect presence or absence of an input voltage to the
heater on paths from the first relay to the heater and from the
second relay to the heater, and a relay control unit configured to
output control signals for turning on and off respective ones of
the first relay and the second relay, wherein the relay control
unit determines that the second relay has failed when the input
voltage is detected by the voltage detection unit in a state in
which the first relay is on and the second relay is off, and the
relay control unit determines that the first relay has failed when
the input voltage is detected by the voltage detection unit in a
state in which the first relay is off and the second relay is
on.
[0012] Accordingly, a second aspect of the present invention
provides a relay control apparatus included in an image forming
apparatus comprising a heater configured to be supplied with
electrical power from a power source, a first relay and a second
relay configured to be each connected between the power source and
the heater, and a voltage detection unit configured to detect
presence or absence of an input voltage to the heater on paths from
the first relay to the heater and from the second relay to the
heater, comprising a first control unit configured to, before
starting passage of electric current through the heater, output a
control signal to turn on the first relay, and when the input
voltage is not detected by the voltage detection unit, output a
control signal to turn on the second relay, a first determination
unit configured to determine that the second relay has failed in a
case where the input voltage is detected by the voltage detection
unit when the first relay is turned on by the first control unit, a
second control unit configured to, before ending passage of
electric current through the heater, output a control signal to
turn off the first relay, and when the input voltage is not
detected by the voltage detection unit, output a control signal to
turn off the second relay, and a second determination unit
configured to determine that the first relay has failed in a case
where the input voltage is detected by the voltage detection unit
when the first relay is turned off by the second control unit.
[0013] According to the present invention, in a circuit
configuration in which the relays are connected to the respective
both ends of the fixing heater, contact fusion occurring in the
respective relays can be individually detected. Moreover, because
contact fusion is detected for one of the relays when it is on, and
for the other one of the relays when it is off, the time required
to detect contact fusion of the two relays can be reduced.
[0014] Further features of the present invention will become
apparent from the following description of exemplary embodiments
(with reference to the attached drawings).
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a cross-sectional view showing a general
arrangement of a full-color printer which is an exemplary image
forming apparatus according to an embodiment of the present
invention.
[0016] FIG. 2 is a block diagram showing a general arrangement of a
control unit in the printer in FIG. 1.
[0017] FIG. 3 is a diagram showing a general arrangement and a
connecting relation of a heater power-feed circuit in FIG. 2.
[0018] FIG. 4A is a flowchart I showing the flow of a process for
detecting contact fusion of first and second relays, and FIG. 4B is
a flowchart II showing the flow of the process for detecting
contact fusion of the first and second relays.
DESCRIPTION OF THE EMBODIMENTS
[0019] The present invention will now be described in detail with
reference to the drawings showing an embodiment thereof.
[0020] FIG. 1 is a cross-sectional view showing a general
arrangement of a full-color printer which is an exemplary image
forming apparatus according to an embodiment of the present
invention.
[0021] Referring to FIG. 1, the full-color printer (hereafter
referred to merely as the "printer") has the following four image
forming units: an image forming unit 1Y for forming yellow-color
images, an image forming unit 1M for forming magenta-color images,
an image forming unit 1C for forming cyan-color images, and an
image forming unit 1Bk for forming black-color images. The image
forming units 1Y, 1M, 1C, and 1Bk are arranged in a row at regular
intervals.
[0022] In the image forming units 1Y, 1M, 1C, and 1Bk, drum-shaped
electrophotographic photosensitive units (hereafter referred to as
the "photosensitive drums") 2a, 2b, 2c, and 2d which are image
carriers are disposed. Primary chargers 3a, 3b, 3c, and 3d,
developing devices 4a, 4b, 4c, and 4d, and transfer rollers 5a, 5b,
5c, and 5d, which are transfer units, and drum cleaner units 6a,
6b, 6c, and 6d are disposed around the respective the
photosensitive drums 2a, 2b, 2c, and 2d. An exposure unit 7 is
placed at a lower portion between the primary chargers 3a to 3d and
the developing devices 4a to 4d.
[0023] The developing devices 4a to 4d store yellow toner, cyan
toner, magenta toner, and black toner, respectively.
[0024] The photosensitive drums 2a to 2d have photoconductive
layers on drum bases which are negatively-charged OPC
photosensitive units and made of aluminum, and rotatively driven by
a drive unit (not shown) in directions indicated by arrows
(clockwise as viewed in FIG. 1) at a predetermined process
speed.
[0025] The primary chargers 3a to 3d, which are primary charging
units, uniformly charge surfaces of the photosensitive drums 2a to
2d to a predetermined negative potential by charging biases applied
from charging bias power sources (not shown).
[0026] The developing devices 4a, 4b, 4c, and 4d have toner
therein, and attach toners of the respective colors to
electrostatic latent images formed on the photosensitive drums 2a
to 2d to develop (visualize) them as toner images.
[0027] The transfer rollers 5a to 5d, which are primary transfer
units, are disposed so as to be brought into abutment with the
respective photosensitive drums 2a to 2d in respective primary
transfer areas 32a to 32d via an intermediate transfer belt 8.
[0028] The drum cleaner units 6a, 6b, 6c, and 6d each have a
cleaning blade for removing transfer residual toner remaining on
the photosensitive drums 2a to 2d after primary transfer from the
photosensitive drums 2a to 2d, and others.
[0029] The intermediate transfer belt 8 is disposed on an upper
surface side of the photosensitive drums 2a to 2d, and tightly
stretched between a secondary transfer opposing roller 10 and a
tension roller 11. The secondary transfer opposing roller 10 is
disposed so as to be brought into abutment with a secondary
transfer roller 12 in a secondary transfer area 34 via the
intermediate transfer belt 8. The intermediate transfer belt 8 is
made of a dielectric resin such as a polycarbonate, a polyethylene
terephthalate resin film, or a polyvinylidene fluoride resin
film.
[0030] Moreover, the intermediate transfer belt 8 has a primary
transfer surface (lower flat surface) 8b, which is formed on a side
opposing the photosensitive drums 2a to 2d, inclined with its
secondary transfer roller 12 side down. Namely, the intermediate
transfer belt 8 is movably opposed to upper surfaces of the
photosensitive drums 2a to 2d, and has the primary transfer surface
8b, which is formed on the side opposing the photosensitive drums
2a to 2d, with its secondary transfer area 34 side down.
Specifically, the inclination angle is set at about 15 degrees.
[0031] Moreover, the intermediate transfer belt 8 is tightly
stretched by the secondary transfer opposing roller 10, which is
disposed on the secondary transfer area 34 side and applies driving
force to the intermediate transfer belt 8, and the tension roller
11 which is opposed to the secondary transfer opposing roller 10
across the primary transfer parts 32a to 32d and applies tension to
the intermediate transfer belt 8.
[0032] The secondary transfer opposing roller 10 is disposed so as
to be able to abut on the secondary transfer roller 12 in the
secondary transfer area 34 via the intermediate transfer belt 8. A
belt cleaning unit 13, which removes and collects transfer residual
toner remaining on a surface of the intermediate transfer belt 8,
is disposed outside the intermediate transfer belt 8 and in the
vicinity of the tension roller 11. A fixing unit 16 is disposed in
a vertical path configuration at a location downstream of the
secondary transfer area 34 in a direction in which a transfer
material (recording material) P is conveyed.
[0033] An exposure unit 7 is comprised of a laser emission unit,
which emits light according to time-series electric digital pixel
signals of given image information, a polygon lens, a reflex
mirror, and so on. By exposing the photosensitive drums 2a to 2d to
light, the exposure unit 7 forms electrostatic latent images of the
respective colors according to image information on surfaces of the
photosensitive drums 2a to 2d charged by the respective primary
chargers 3a to 3d.
[0034] Next, a description will be given of a one-sided image
forming operation performed by the printer in FIG. 1.
[0035] Upon an image formation start signal being issued, the
photosensitive drums 2a to 2d of the respective image forming units
1Y to 1Bk, which are rotatively driven at a predetermined process
speed, are uniformly charged to negative polarity by the respective
primary chargers 3a to 3d. Then, the exposure unit 7 applies a
color-separated image signal input from outside from a laser light
emitting element, and thus forms electrostatic latent images of the
respective colors on the respective photosensitive drums 2a to 2d
via the polygon lens, the reflex mirror, and so on.
[0036] Then, the developing device 4a to which a developing bias of
the same polarity as the charging polarity (negative polarity) of
the photosensitive drum 2a is applied attaches yellow toner to the
electrostatic latent image formed on the photosensitive drum 2a,
and thus visualizes the electrostatic latent image as a toner
image. In the primary transfer area 32a between the photosensitive
drum 2a and the transfer roller 5a, the yellow toner image is
primarily transferred onto the intermediate transfer belt 8 by the
transfer roller 5a to which a primary transfer bias (opposite in
polarity to the toner (positive polarity)) is applied.
[0037] The intermediate transfer belt 8 onto which the yellow toner
image has been transferred is moved toward the image forming unit
1M. Then, in the image forming unit 1M as well, a magenta toner
image formed on the photosensitive drum 2b in the same way as
described above is superimposed on the yellow toner image on the
intermediate transfer belt 8 in the primary transfer area 32b. On
this occasion, transfer residual toner remaining on the
photosensitive drums 2a to 2d is scraped off and collected by the
cleaning blades or the like provided in the drum cleaning units 6a
to 6d.
[0038] Thereafter, in the same way, cyan and black toner images
formed on the photosensitive drums 2c and 2d of the image forming
units 1C and 1Bk are sequentially superimposed on the yellow and
magenta toner images transferred onto the intermediate transfer
belt 8 in superimposed manner in the respective primary transfer
areas 32c and 32d. Thus, full-color toner images are formed on the
intermediate transfer belt 8.
[0039] Then, a leading end of the full-color toner images on the
intermediate transfer belt 8 is moved to the secondary transfer
area 34 between the secondary transfer opposing roller 10 and the
secondary transfer roller 12. In accordance with this timing, a
transfer material P selectively fed from a sheet feed cassette 17
or a manual feed tray 20 via a conveying path 18 is conveyed to the
secondary transfer part 34 by registration rollers 19.
[0040] The full-color toner images are secondarily transferred onto
the transfer material P, which has been conveyed to the secondary
transfer part 34, in a collective manner by the secondary transfer
roller 12 to which a secondary transfer bias (opposite in polarity
to the toner (positive polarity)) is applied.
[0041] The transfer material P bearing the full-color toner images
is conveyed to the fixing unit 16, which thermally fixes the
full-color toner images on a surface of the transfer material P by
heating and pressurizing the transfer material P. The transfer
material P is then discharged onto a discharged sheet tray 22 by
sheet discharging rollers 21, which completes the sequential image
forming operation. It should be noted that secondary transfer
residual toner or the like remaining on the intermediate transfer
belt 8 is removed and collected by the belt cleaning unit 13.
[0042] Next, a description will be given of a double-sided image
forming operation performed by the printer in FIG. 1.
[0043] The procedure for the double-sided image forming operation
is the same as for the one-sided image forming operation before the
point where the transfer material P is conveyed to the fixing unit
16, and the full-color toner images are heated and pressurized to
be thermally fixed on the surface of the transfer material P. After
that, the rotation of the sheet discharging rollers 21 is stopped
in a state in which a major portion of the transfer material P has
been discharged onto the discharged sheet tray 22 on an upper side
of the main body by the sheet discharging rollers 21. On this
occasion, a trailing end of the transfer material P has reached an
invertible position 42.
[0044] Subsequently, the sheet discharging rollers 21 are reversely
rotated so as to feed the transfer material P, the conveyance of
which has been stopped by stopping the rotation of the sheet
discharging rollers 21, into a double-sided path having
double-sided rollers 40 and 41. By reversely rotating the sheet
discharging rollers 21, the trailing end of the transfer material P
which has been positioned at the invertible position 42, becomes a
leading end and reaches the double-sided rollers 40. After that,
the transfer material P is conveyed to the double-sided rollers 41
by the double-sided rollers 40, and sequentially conveyed toward
the registration rollers 19 by the double-sided rollers 40 and 41.
In the meantime, an image formation start signal is output, and the
same operation as in the one-sided image forming operation
described above is carried out. Specifically, the transfer material
P is moved to the secondary transfer area 34 by the registration
rollers 19 in accordance with the timing in which the leading end
of the full-color toner images on the intermediate transfer belt 8
is moved to the secondary transfer area 34 between the secondary
transfer opposing roller 10 and the secondary transfer roller
12.
[0045] In the secondary transfer area 34, the leading end of the
toner images and the leading end of the transfer material P are
matched together, and the toner images are transferred onto the
transfer material P. After that, the toner images on the transfer
material P are fixed by the fixing unit 16 as with the one-sided
image forming operation. Then, the transfer material P is conveyed
again by the sheet discharging rollers 21, and eventually
discharged onto the discharged sheet tray 22, which completes the
sequential image forming operation.
[0046] FIG. 2 is a block diagram showing a general arrangement of a
control unit in the printer in FIG. 1. It should be noted that in
FIG. 2, only parts relating to the present invention and main
functional units are illustrated, and other component elements and
functional units are omitted.
[0047] Referring to FIG. 2, the control unit 110 is a basic control
unit that controls the entire printer, and has a CPU 171, a ROM
174, and a RAM 175. The ROM 174 stores control programs and others.
The RAM 175 is used as a work memory when the CPU 171 executes
control programs. The CPU 171 is connected to the ROM 174 and the
RAM 175 via an address bus and a data bus.
[0048] The CPU 171 is connected to sensors (not shown) for
detecting various loads (not shown) such as motors and clutches and
sheet positions, and a temperature detection circuit 700 via an I/O
port 173. The fixing unit 16 and a heater power-feed circuit 500
that supplies electrical power of an AC power source 550 to a
fixing heater (not shown) in the fixing unit 16 are connected to
the I/O port 173, and the CPU 171 controls them. Specifically, by
executing control programs read out from the ROM 174, the CPU 171
sequentially controls input and output via the I/O port 173, and
controls the temperature of the fixing heater in the fixing unit
16.
[0049] A temperature detection signal output from a temperature
sensor (not shown) in the fixing unit 16 is input to the
temperature detection circuit 700 via the I/O port 173. The
temperature detection circuit 700 outputs control signals to the
heater power-feed circuit 500.
[0050] The CPU 171 is connected to a console 172 having a display
unit (not shown), which produces screen displays, and a key input
unit (not shown), and controls screens displayed on the console 172
and key inputs. By operating the key input unit, an operator
instructs the CPU 171 to switch between image forming operation
modes and screen displays. As a result, the CPU 171 displays
operation mode settings according to printer conditions and key
inputs.
[0051] The CPU 171 is also connected to an external I/F processing
unit 200, an image memory unit 300, and an image forming unit 400.
It should be noted that the image forming units 1Y, 1M, 1C, and 1Bk
are included in the image forming unit 400.
[0052] The external I/f processing unit 200 sends and receives
image data and processing data from external devices such as a PC.
The image memory unit 300 carries out an image expansion process
and a temporary image storage process. The image forming unit 400
has the image forming units 1Y, 1M, 1C, and 1Bk described above,
and carries out a process in which it causes the exposure unit 7 to
expose line image data, which has been transferred from the image
memory unit 300, to light.
[0053] FIG. 3 is a diagram showing a general arrangement and a
connecting relation of the heater power-feed circuit 500 in FIG.
2.
[0054] The fixing unit 16 has a fixing heater 601, which is a heat
source for heating and fixing toner images, and a temperature
sensor 602 such as a thermistor, which is disposed in the vicinity
of the fixing heater 601, for detecting the temperature of the
fixing heater 601. It should be noted that the fixing unit 16 has a
pressurizing roller and others, description of which is
omitted.
[0055] The temperature sensor 602, which is a temperature detection
unit, is connected to the control unit 110 and the temperature
detection circuit 700. A temperature detection signal 604 output
from the temperature sensor 602 is input to the control unit 110
and the temperature detection circuit 700. The fixing heater 601
has both ends thereof connected to the heater power-feed circuit
500.
[0056] The heater power-feed circuit 500 has a first relay 501 and
a second relay 502 for supplying/interrupting electrical power
supplied from the AC power source 550 to both ends of the fixing
heater 601. The first relay 501 has one end thereof connected to
one end of the fixing heater 601, and the other end thereof
connected to the AC power source 550. The second relay 502 has one
end thereof connected to the other end of the fixing heater 601 via
a semiconductor SW 510, and the other end thereof connected to the
AC power source 550. The first relay 501 and the second relay 502
are controlled to be on and off by control signals 503 and 504
output from the control unit 110, which is a relay control unit.
The control signals 503 and 504 output from the control unit 110
are input to a first AND circuit 702 and a second AND circuit 703,
respectively, via the I/O port 173 in FIG. 2 described above.
[0057] A zero cross detection circuit 505 is connected in parallel
to the fixing heater 601 and the AC power source 550 as illustrated
in the figure. Upon being supplied with electrical power from the
AC power source 550, the zero cross detection circuit 505 outputs a
zero cross signal 506 (a detection signal) according to zero cross
timing of an alternating waveform to the control unit 110 (a
voltage detection unit). The zero cross signal 506 output from the
zero cross detection circuit 505 is input to the control unit 110
via the I/O port 173 in FIG. 2 described above.
[0058] The semiconductor SW 510 is a semiconductor switch such as a
triac (registered trademark), which is disposed on a path for
supplying electrical power to the fixing heater 601, and capable of
turning on and off power feeding to the fixing heater 601
irrespective of whether the first relay 501 and the second relay
502 are turned on or off. The semiconductor SW 510 is controlled to
be on or off in response to a control signal 512 output from the
control unit 110.
[0059] The control unit 110 outputs the control signal 512 in
response to the temperature detection signal 604 from the
temperature sensor 602. By controlling the semiconductor SW 510 to
be on or off, the temperature of the fixing heater 601 is
controlled.
[0060] The first AND circuit 702 is a logic circuit that performs
logical conjunction (AND) based on the control signal 503 output
from the control unit 110 and a control signal 701 output from the
temperature detection circuit 700, and outputs a first AND signal
704 to the first relay 501. On the other hand, the second AND
circuit 703 is a logic circuit that performs logical conjunction
(AND) based on the control signal 504 output from the control unit
110 and the control signal 701 output from the temperature
detection circuit 700, and outputs a second AND signal 705 to the
second relay 502. Thus, when a control signal for turning off the
first relay 501 and the second relay 502 is output from one or both
of the control unit 110 and the temperature detection circuit 700,
both relays are turned off.
[0061] The control unit 110 controls the temperature of the fixing
heater 601 based on the temperature detection signal 604 from the
temperature sensor 602. When determining that the temperature of
the fixing heater 601 indicated by the temperature detection signal
604 is not less than a threshold value Tmax1, the control unit 110
determines that the fixing heater 601 has increased from a proper
temperature, and stops power feeding to the fixing heater 601.
Specifically, the control unit 110 outputs the control signal 512
for turning off the semiconductor SW 510 and outputs the control
signals 503 and 504 for turning off the first relay 501 and the
second relay 502.
[0062] On the other hand, the temperature detection circuit 700
functions as a heater temperature abnormality detection unit, and
is able to stop power feeding to the fixing heater 601 based on the
temperature detection signal 604 from the temperature sensor 602.
Specifically, when determining that the temperature of the fixing
heater 601 indicated by the temperature detection signal 604 is not
less than a threshold value Tmax2, the temperature detection unit
700 determines that the fixing heater 601 is abnormally heating,
and outputs the control signal 701 for stopping power feeding to
the fixing heater 601.
[0063] Because the temperature detection circuit 700 outputs the
control signal 701 for turning off the first AND circuit 702 and
the second AND circuit 703, no signal for turning on the first
relay 501 and the second relay 502 is output even if the control
signals 503 and 504 for turning off the first relay 501 and the
second relay 502 are input from the control unit 110. As a result,
the first relay 501 and the second relay 502 are turned off, and
power feeding to the fixing heater 601 is stopped.
[0064] The above described threshold values Tmax1 and Tmax2 have
the following relationship, Tmax2>Tmax1. Thus, even when
temperature cannot be controlled due to some abnormal condition
such as runaway occurring in the CPU 171 in the control unit 110,
power feeding to the fixing heater 601 can be stopped by the
temperature detection circuit 700. As a result, the fixing heater
601 and its surrounding components can be protected, and abnormal
fixing can be prevented.
[0065] FIGS. 4A and 4B are flowcharts showing the flow of a process
for detecting contact fusion of the first and second relays.
[0066] As shown FIG. 4A, the control unit 110 determines in step
S201 whether or not to start passing electric current through the
fixing heater 601. When determining to start the passage of
electric current, the control unit 110 outputs the control signal
503 for turning on the first AND circuit 702, and turns on the
first relay 501 in response to the first AND signal 704 output from
the first AND circuit 702 (step S202). After that, the control unit
110 stands by for a predetermined time period (for example, 100 ms)
(step S203). This aims at keeping contact connection stable because
the first relay 501 is a mechanical relay.
[0067] Then, in step S204, the control unit 110 determines whether
or not it has detected the zero cross signal 506 from the zero
cross detection circuit 505. When the control unit 110 has detected
the zero cross signal 506 (YES in the step S204), the control unit
110 proceeds to step S205.
[0068] In the step S205, the control unit 110 determines that
electric current is being passed through the second relay 502 due
to a failure such as contact fusion because the zero cross signal
506 is detected even though the control unit 110 has not output the
control signal 504 for turning on the second relay 502. The step
S205 is an exemplary first determination unit. Then, the control
unit 110 stops the operation of the printer in FIG. 1 (step S217),
and causes the display unit on the console 172 to display an error
message (step S218), followed by terminating the process.
[0069] On the other hand, when in the step S204, the control unit
110 has not detected the zero cross signal 506, (NO in the step
S204), the control unit 110 proceeds to step S206.
[0070] In the step S206, the control unit 110 outputs the control
signal 504 for turning on the first AND circuit 703, and turns on
the second relay 502 in response to the second AND signal 705
output from the second AND circuit 703. The step S206 is an
exemplary first control unit. After turning on the second relay
502, the control unit 110 stands by for a predetermined time period
(for example, 100 ms) (step S207). The reason for this is the same
as in the step S203 described above.
[0071] Then, in the step S208, the control unit 110 determines
whether or not it has detected the zero cross signal 506 from the
zero cross detection circuit 505. When the control unit 110 has not
detected the zero cross signal 506 (NO in the step S208), the
control unit 110 proceeds to step S209.
[0072] In the step S209, the control unit 110 determines that
electric current is not being passed through the first relay 501
and the second relay 502 due to a failure such as poor conduction
because electric current is not being passed through the first
relay 501 and the second relay 502 even though the first relay 501
and the second relay 502 are turned on. This failure can be
detected irrespective of whether poor conduction occurs in one of
the first relay 501 and the second relay 502 or both the first
relay 501 and the second relay 502. The step S209 is an exemplary
third determination unit. When determining that a failure such as
poor conduction has occurred, the control unit 110 carries out the
processes in the step S217 and the subsequent steps, followed by
terminating the present process.
[0073] On the other hand, in the step S208, when detecting the zero
cross signal 506, the control unit 110 determines that the first
relay 501 and the second relay 502 properly work, and starts
passing electric current through the fixing heater 601 (step S210),
which enables an image forming operation to be carried out. In the
step S210, the control unit 110 stars passing electric current
through the fixing heater 601 by outputting the control signal 512
for turning on the semiconductor SW 510.
[0074] Referring to FIG. 4B, upon the image forming operation being
completed, the control unit 110 determines whether or not to end
the passage of electric current through the fixing heater 601 (step
S211). When determining to end the passage of electric current, the
control unit 110 outputs the control signal 503 for turning off the
first AND circuit 702, and turns off the first relay 501 in
response to the first AND signal 704 output from the first AND
circuit 702 (step S212). After that, the control unit 110 stands by
for a predetermined time period (for example, 100 ms) (step S213),
and then determines whether or not it has detected the zero cross
signal 506 (step S214). When detecting the zero cross signal 506
(YES in the step S214), the control unit 110 proceeds to step
S215.
[0075] In the step S215, the control unit 110 determines that
electric current is being passed through the first relay 501 due to
a failure such as contact fusion because the zero cross signal 506
is detected even though the control unit 110 has not output the
control signal 503 for turning on the first relay 501. The step
S215 is an exemplary second determination unit. Then, the control
unit 110 carries out the processes in the step S217 and the
subsequent steps, followed by terminating the present process.
[0076] On the other hand, when in the step S214, the control unit
110 has not detected the zero cross signal 506, (NO in the step
S214), the control unit 110 proceeds to step S216.
[0077] In the step S216, the control unit 110 outputs the control
signal 504 for turning off the second AND circuit 703, and turns on
the second relay 502 in response to the second AND signal 705
output from the second AND circuit 703. The step S216 is an
exemplary second control unit. It should be noted that the above
described process can be applied to a case where the locations of
the first relay 501 and the second relay 502 are reversed.
[0078] After the passage of electric current is started in the step
S210, the temperature detection circuit 700 stops power feeding to
the fixing heater 601 based on the temperature detection signal 604
from the temperature sensor 602. Specifically, when determining
that the temperature of the fixing heater 601 detected by the
temperature sensor 602 is not less than the threshold value Tmax2,
the control unit 110 determines that the fixing heater 601 is
abnormally heating, and outputs the control signal 701 for stopping
power feeding to the fixing heater 601.
[0079] After the passage of electric current is started in the step
S210, the temperature detection circuit 700 also stops power
feeding to the fixing heater 601 based on the temperature detection
signal 604 from the temperature sensor 602. Specifically, when
determining that the temperature of the fixing heater 601 detected
by the temperature sensor 602 is not less than the threshold value
Tmax1, the control unit 110 determines that the fixing heater 601
has increased from a proper temperature, and outputs the control
signals 503 and 504 for stopping power feeding to the fixing heater
601.
[0080] According to the above described embodiment, before starting
the passage of electric current through the fixing heater 601, the
control unit 110 outputs a control signal to turn on the first
relay 501, and when no input voltage has been detected by the zero
cross detection circuit 505, outputs a control signal to turn on
the second relay 502. In a case where an input voltage is detected
by the zero cross detection circuit 505 when the first relay 501 is
turned on, the control unit 110 determines that the second relay
502 has failed. Moreover, before ending the passage of electric
current through the fixing heater 601, the control unit 110 outputs
a control signal to turn off the first relay 501, and when no input
voltage has been detected by the zero cross detection circuit 505,
outputs a control signal to turn off the second relay 502. In a
case where an input voltage is detected by the zero cross detection
circuit 505 when the first relay 501 is turned off, the control
unit 110 determines that the first relay 501 has failed. Thus, in
the circuit configuration in which the relays are connected to the
respective both ends of the fixing heater, contact fusion of the
respective relays can be individually detected.
[0081] As described above, by staggering the operation timing of
the two relays, contact fusion of each relay can be reliably
detected. As a result, the time required for detecting contact
fusion of the two relays can be reduced because the presence or
absence of contact fusion is detected for one of the relays when it
is on, and the presence or absence of contact fusion is detected
for the other one of the relays when it is off.
Other Embodiments
[0082] Aspects of the present invention can also be realized by a
computer of a system or apparatus (or devices such as a CPU or MPU)
that reads out and executes a program recorded on a memory device
to perform the functions of the above-described embodiment(s), and
by a method, the steps of which are performed by a computer of a
system or apparatus by, for example, reading out and executing a
program recorded on a memory device to perform the functions of the
above-described embodiment(s). For this purpose, the program is
provided to the computer for example via a network or from a
recording medium of various types serving as the memory device
(e.g., computer-readable medium).
[0083] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0084] This application claims the benefit of Japanese Patent
Application No. 2010-106404 filed May 6, 2010, which is hereby
incorporated by reference herein in its entirety.
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